Purpose: To examine the genotype of STm 135a isolates and the relationship between their phenotype and survival in the processing environment, particularly resistance to sanitisers used in commercial poultry production.
Methods: Thirty-six broiler chicken isolates of STm 135a from across Australia were typed by multi-locus variable number tandem repeat analysis (MLVA) and screened for Congo red binding and aggregative colony morphology (T medium). The ability to produce GVVPQ fimbriae was evaluated by detection and sequencing of a fragment of agfA, the structural gene for SEF 17 fimbrin. The survival of the isolates in simulated immersion chiller conditions to various antimicrobials (6 ppm free chlorine, 50 ppm peracetic acid and 1% v/v lactic acid) was also investigated by a microdilution method.
Results: All strains examined were representative of five different MLVA types. Further, all isolates expressed fimbriae (F+), although production varied depending on incubation temperature. The agfA gene was detected in all isolates and sequence analysis revealed ≥ 98% similarity. STm 135a cells, whether fimbriated or not, were readily injured within 10 mins by working concentrations of sodium hypochlorite and peracetic acid. When chicken skin was added to the chiller system, survival increased.
Significance: As a direct relationship between fimbriation of STm 135a and survival in simulated chicken processing was not evident in this study, other ecological factors should be considered in future studies.